Research on the regeneration of axons in the long fiber tracts of mammalian spinal cord would benefit from the development of an effective experimental model. We plan to analyze the regenerative capacity of rat dorsal root ganglion cells in order to provide the fundamental base of information required to develop such an experimental model. The dorsal root ganglion cell was chosen because it innervates both the central nervous system and periphery. Furthermore, these cells send axons in both myelinated and unmyelinated fiber tracts of the spinal cord, the dorsal columns and tract of Lissauer respectively. The regenerative capacity of both central and peripheral branches of adult rat L-4 dorsal root ganglion cells will be analyzed. We will use radioactive precursors to label the ganglion cell axons by axonal transport and measure the latency and rate of axonal regeneration in the dorsal root and sciatic nerve. After characterizing the properties of regeneration of the axons in the dorsal root, we will evaluate the capacity of these axons to continue regenerating from the dorsal root into the spinal cord. For this analysis anterograde autoradiographic tracing will be used, and the newly regenerated axons will be mapped with the light and electron microscope. Whether or not the axons regenerate into the spinal cord, we will have a valuable model for studying regeneration. For example, if the axons stop growing when they reach the spinal cord, we will be able to analyze the factors which stop the axons from regenerating. However, if the axons regenerate into the spinal cord, we will be able to study the regeneration of axons in adult mammalian spinal cord and determine whether the dorsal root axons regenerate into the long ascending fiber tracts when the spinal cord is not damaged directly. This project can contribute to our understanding of central nervous system regeneration at two levels: 1) by developing an experimental model so that axonal regeneration can be studied in the mammalian spinal cord and 2) by employing this model to compare the mechanisms involved in the regeneration of axons in the central and peripheral nervous system.